Implement cursor changing on Mushrome

ui/display/manager/display_manager.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/display/manager/display_manager.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <map>
@@ skipping 679 matching lines @@
     const DisplayLayout& layout =
         layout_store_->GetRegisteredDisplayLayout(list);
     current_default_multi_display_mode_ =
         (layout.default_unified && unified_desktop_enabled_) ? UNIFIED
                                                              : EXTENDED;
   }
 
   if (multi_display_mode_ != MIRRORING)
     multi_display_mode_ = current_default_multi_display_mode_;
 
-  CreateSoftwareMirroringDisplayInfo(&new_display_info_list);
-
   // Close the mirroring window if any here to avoid creating two compositor on
   // one display.
   if (delegate_)
     delegate_->CloseMirroringDisplayIfNotNecessary();
 
+  CreateSoftwareMirroringDisplayInfo(&new_display_info_list);

[sadrul, 2017/06/14 03:03:56]

This seems somewhat subtle. One of the ui/display owners should review this.

[Elliot Glaysher, 2017/06/15 17:35:07]

Yes, the bug here is that CloseMirroringDisplayIfNotNecessary() can access
display information. If you first call CreateSoftwareMirroringDisplayInfo(), you
get into a state where there is stale references to the current mirror display.

[oshima, 2017/06/15 18:16:17]

This was moved in this CL (https://codereview.chromium.org/1133323002), but it's
before ozone era.
I need to refresh my memory and dig code/bugs. Please give me some time.

[oshima, 2017/06/19 19:17:55]

Which reference becomes stale?

+
   Displays new_displays;
   Displays removed_displays;
   std::map<size_t, uint32_t> display_changes;
   std::vector<size_t> added_display_indices;
 
   Displays::iterator curr_iter = active_display_list_.begin();
   DisplayInfoList::const_iterator new_info_iter = new_display_info_list.begin();
 
   while (curr_iter != active_display_list_.end() ||
          new_info_iter != new_display_info_list.end()) {
@@ skipping 782 matching lines @@
 }
 
 const Display& DisplayManager::GetSecondaryDisplay() const {
   CHECK_LE(2U, GetNumDisplays());
   return GetDisplayAt(0).id() == Screen::GetScreen()->GetPrimaryDisplay().id()
              ? GetDisplayAt(1)
              : GetDisplayAt(0);
 }
 
 }  // namespace display